Animal Behaviour *
By JULIAN HUXLEY ANIMAL behaviour is a subject of extreme complexity. After its initial stage of anecdotage, various attempts have been made to render it more scientific. Some of these attempts have pinned their faith to rigid experimental methods ; others to a thoroughgoing physiological analysis, while still others have based themselves on a comparative evolutionary study of the mechanisms of behaviour—sense-organs, nervous system, and muscular mechanisms.
* The Behaviour of Animals : An Introduction to its Study. By E. S. Russell. (Arnold, 10s. 6d.)
Along these lines, biologists have arrived at certain broad generalizations—the tropism theory, the concept of the conditioned reflex, the theories that learning is a trial and error process, the .rigid mechanical view of instinct as some- thing wholly alien to intelligence. But it is highly probable that all these generalizations are either premature or partial. Dr. Russell, in this agreeably-written and stimulating little book, points out one of the chief reasons for their incom- pleteness. It is that the ecological viewpoint has not been sufficiently stressed : and the ecological point of view demands the study of animals in relation to their normal surroundings and mode of life. When an animal orientates its direction of movement in response to the direction from which light falls upon it, we speak of the reaction as a tropism : and Loeb and others have given a mechanistic explanation of such tropisms, which in some cases at least appear to hold good. But here the mechanistic analysis Comes to a full stop. It finds it, for instance, very difficult to give an explanation for the fact that tadpoles in a large aquarium swim at random, while, if imprisoned in a small glass jar in the same aquarium, they became positively phototropic and attempt to swim towards the light. As Dr. Russell points out, this fact acquires significance if we regard it as part of an escape-mechanism : when alarmed or confined, the animals seek to escape towards the light, which is normally
• the road to the open and to safety.
The author's main thesis is as follows. The behaviour of an animal is always connected with the satisfaction of its needs, whether these be positive ones like the securing of a mate, or more negative like getting back again into optinnun conditions if removed from its proper "ecological niche." Further, this behaviour is always conative, never purely mechanical : it strives towards a goal, and if one method fails will try another. In so far as the behaviour is determined, it is determined not merely by external stimuli, but by the needs of the animal. There is no sharp line between instinct and intelligence : there is only a lesser or a greater degree of plasticity in behaviour. To understand behaviour properly, the normal ecology of the animal must be known and borne constantly in mind : laboratory experi- ments should take account of the animal's normal way of life—abnormal conditions will give misleading results. Finally, behaviour is always an integrated whole : it cannot be regarded as the sum of a number of separate reflexes or other factors.
There is a great deal of truth in these contentions, and Dr. Russell brings forward many interesting facts in their support—such as the previously mentioned facts about tropisms ; or the adjustment of the dung-beetle's or the ant-lion's highly specialized instincts to experimental inter- ference with their dung-ball or prey ; or the general aban- donment by biologists of the conclusions on learning drawn by Thorndike from his very artificial experiments on cats, in contrast with the success of Kiihler's much simpler type of experiment with apes, which was, however, adapted to their mode of life. He also gives numerous excellent examples of the fact that behaviour is a response to internal needs as much as to external stimuli. • While this method of attack is of impeccable breadth, and often salutary, it seems to peter out when we attempt deep or precise analysis. Dr. Russell has made the mistake of so many of his predecessors in the field, in thinking that any one method or set of ideas will provide the ultimate clue. Purely physiological analysis may be futile by itself, or in conjunction with a merely surnmative theory of behaviour, but it is indispensable for understanding the machinery of behaviour. Instincts may possess a certain degree of plas- ticity: but they are often rigid to a degree almost incon- ceivable to the layman (Dr. Russell gives several excellent examples of this, such as the wasp which normally lives on bark, and elaborately camouflaged her nest to resemble bark— even when she happened to build it on an Archdeacon's mantel- piece), and this rigidity is undoubtedly mechanistic in the sense of being predetermined within narrow limits by heredity.
He makes a great mystery of the fact that many instinctive actions, such as the hiding or crouching of young game-bird chicks at the mother's warning note, are anticipatory, in the sense of fraying reference to something which is about to happen or is likely to happen, although their performers can have no inkling of this end. "Why this should be so," he says, "is one of the many unsolved problems of instinct." On the contrary, the great majority of biologists would assert that it is what any reasonable person would expect. Since instinctive acts have a hereditary basis, they can be modified by natural selection. Those strains of game-birds of which the chicks did not have this anticipatory instinct would be at a disadvantage : the mystery turns into a commonplace of evolutionary mechanism, on precisely the same footing as any other adaptation.
In general, he pays little attention to the evolutionary aspect of behaviour ; but even if the striving towards a goal and the adoption of different means to reach it are as universal as he maintains, there is a change in the amount of plasticity between lower and higher animals, and one of the most inter- esting chapters in the subject is the study of the measure of that change and the physical machinery which has brought it about.
Another criticism of general import must be mentioned. Dr. Russell frequently contrasts the needs of an animal with the stimuli which affect it. But there is no such hard-and-fast distinction. The needs make themselves felt by stimuli, which merely happen to be internal instead of external. A hungry man only knows he is hungry because his stomach is sending a particular set of impulses to his brain : an animal knows it is upside-down because of messages from the receptors in its muscles and from its inner ear : a bird seeks its mate at one season and not at another because its system at the former is flooded with special hormones.
But, as I said at the outset, animal behaviour is a subject of great complexity. It is also a young subject, and for the moment must, it seems, progress by stress now on this aspect, now on that. Dr. Russell has done well to stress the ecological aspect of animal behaviour and all its applications. The pro- fessional biologist will profit from reading this book, and the layman will find it, with its lucid presentation and its wealth of interesting and entertaining illustration, often taken from first-hand experience,- an excellent introduction to further study a the subject.
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